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Full text of "The Cambridge Natural History"

PHENACODUS

and not climbing  or  grasping  organs;   the   number  of toes be-
comes  reduced,  and culminates  twice  (in  the  horse and in  the

Latopterna) in one toe
on each foot ; at the
same time the ulna be-
comes rudimentary and
fuses with the radius,
and the fibula in the
hind-limb undergoes a
like reduction. The
clavicle is absent even
in some of the oldest
types ; its presence in
Typotherium * is highly
remarkable. The tail
too, an organ which is
long in some of the
early forms, gets short
in their modern deriva-
tives.

Coupled with the in-
creasing perfection of the
Jf   foot   as   an   organ   used
  merely  for   the   support
   of the body, certain in-
"j5   teresting    changes    have
o   taken    place   in    the
"^   arrangement    with     re-
&   gard   to   each    other   of
the   several   bonelets   of
the wrist and ankle.    It
has been held by  Cope
and others that the truly
primitive  disposition -of
these bones was that pre-
sented to us by certain

early types, such as MeniscotheTium or the  existing elephant  or
Hyraoo.     In these animals there is (see Fig. 112) a serial arrange-

1 This creature is, howerer, sometimes referred to the neighbourhood of the
Rodents.